Electrophotographic printers



1953 E. K. KAPRELIAN 3, ,4

ELECTROPHOTOGRAPHIC PRINTERS Filed April 26, 1960 4 Sheets-Sheet 1VOLTAGE SOURCE /48 F/GJO NONE I RED BLUE GREEN WH/TE Aug. 13, 1963 FiledApril 2 6. 1960 NONE RED GREENBL JEW/H/TE WHITE LIGHT WH/ E R D E. K.KAPRELIAN ELECTROFHOTOGRAPHIC PRINTERS 4 Sheets-Sheet 2 INVENTOR.

,1963 E. K. KAPRELIAN I 3,100,426

ELECTROPHOTQGRAPHIC PRINTERS 4 Filed April 26, 1960 4 Sheets-Sheet 3 I Il l l l I l I l g I I l I l l l l l I Fie. l6

VOLT 6E IN VEN TOR.

Aug. 13, 1963 E. K. KAPRELIAN ELECTROPHOTOGRAPHIC PRINTERS 4 Sheets-Sheet 4 Filed April 26, 1960 VOLTAGE SOURCE Fie.\3

9K INVENT'OR.

, 3,100,426 ELECTROPHOTOG'RAPHIC PRINTERS 1 Edward K. KapreliamRed BankNJ.

(Rte. 3, Box 14, Joppa, Md.) Filed Apr. 26, 1960,Ser. No. 24,804 8Claims. (Cl. 95-1.7)

This application is a continuation-in-part of application Ser. No.669,866, filed July 3, 1957, and now Patent 2,940,847. r i

This invention relates to improved methods and means for electrostaticcolor photography or color printing.

' In ordinary electrostatic photography orprinting there is formed on aninsulating surface an intermediate electrostatic image, corresponding inpotentials to the lightvalues of the original object, and thiselectrostatic image is rendered visible by dusting with a' suitablepowder which adheres selectively to the surface in a patterncorresponding to the electrostatic image. A description of this processmay be found in US. Patent 2,297,691, issued Oct. 6, 1942, to C. F.Carlson.

It is also possible to practice electrostatic photography 1byilluminating a layer of normally insulating photoconductive powderwhich is located in an electrical field. In this case powder lying inanilluminated area becomes charged and is attracted away to a region ofopposite polarity. -A'description of this process may be found inU.S..Patent 2,758,939, issued Aug. 14, 1956, to M. L.

Sugarman.

Inthe electrophotographic processes of these and other patents of theprior art the action is essentially that of an ordinary monochromatic orblack-and-white system. The basic image is one rendered in monochrome;and it is possible, by utilizing color separation techniques, to producecolor prints or photographs by superimposing in proper registryseparation images employing properly chosen dyes or pigments.

In contrast with previously known systems the present invention producesthe color image directly'in a single step without the use of separationimages. In the practice of this invention the color image is produced bythe selective migration of charged color particles in an electricalfield according to the color ;or wavelength .of the light. r

One of the objects of this-invention is to employ the principles ofelectrostatic electrophotography in the production of color prints.

Another object is to provide a relatively simple, direct and low costarrangement for the production of color photographs, prints, posters andsigns. t

Still another object is the'provision'of-a method and means for thecontinuous production of color prints.

These and other objects will become apparent from the specification anddrawings in which FIG. 1 shows in cross section one form ofphotoconductive color particle.

FIG. 2 shows in cross section another orm of photo conductive colorparticle.

FIG. 3 shows in cross section still another form 0 photoconductive colorparticle. 1

FIG. 4 shows in cross section still another form of photoconductivecolor particle.

FIG. 5 shows in cross section one form of a non-photoconductive colorparticle.

FIG. 6 shows in cross section another form of nonphotoconductiveparticle.

FIG. 7 shows diagrammatically the arrangement of photoconductive colorparticles prior toexposure in one method of the invention. I

FIG. 8 shows diagrammatically the arrangement of the color particles ofFIG. 7 after exposure.

FIG. 9 shows diagrammatically the arrangement of elements for FIG. 12:

electrophotographic prints.

given color. i

'anthracene, and sulfur. powder may be used, and it is preferred thatthe particle 'si zes fall in the range of 2 to 30'microns. The dyedlayer 'may'consist of any suitable dye in gelatin, wax, vinyl orsilicone resin, cellulose ester or similar material in a :7 thicknessoffrom' 4 to 25 microns. The powdered photo- Patented Aug. 13, 1963photoconductive color particles prior to exposure in another method ofthe invention. I

FIG. 10 shows diagrammatically the arrange ent of the color particle ofFIG. 9 after exposure.

FIG. 11' shows diagrammatically the arrangement of non-photoconductivecolor particles prior to exposure in still another method of theinvention.

" FIG. 12 shows diagrammatically the arrangementof'the color particlesof FIG. 11 after exposure.

FIG. 13 shows diagrammatically the relationship of printing from the'color image resulting in FIG. 14 shows diagrammatically the finalarrangement of the color particles in FIG. 13 after exposure.

FIG. 15 shows diagrammatically, one device for producingelectrophotographic prints, sectioned along line 15-15 of FIG. 16.

FIG. 16 is a viewer the device of FIG. 15 taken along line 16 16 of FIG.15; a

FIG." 17 shows another device for the production of FIG. 18 shows infront elevational view another printing device for producingelectrophotographic prints one continuous basis. FIG. 19 shows in sideelevation the device of FIG. 18.

the method of photography described herein. In the use of any of theseparticles the essential action is that in a layer of mixed colorparticles, those particles of a given color will migrate or, ifdesirable, react oppositely by remaining unmoved when subjected to lightof the The color particle 10 of FIGS. 1 and 2 comprises one or more bits12 of asuitable photoconductor surrounded by a layer or coating 14 ofdyed gelatin or similarmaterial. Typical photoconductive materialsinclude selenium, zinc oxide, cadmium sulfide, cad-mium telluride,Actually any photoconductive conductor may bernixed with the dyed layermaterial together with a splvent and then dried while being agitated,

as by a'warmairblast. Spraying of the photoconductorsolvent-dye-layermixture into aheated chamber will also 7 yield 'suitable'particles.""Inforde'r'to increase the photo. graphi'cspe'ed of these particles itmay be necessary'to add to the dyel'ayer a small amount of a suitablesalt to reduce .the electricalresistance of the layer and thereby permitmore rapid charging of the particle.

FIG. 3 shows a particle 16 comprising'a central core .18 which mayconsist of a clear, transparent glass or plastic bead carrying atransparent photoconductive layer 20 :and an outer, dyed, transparentlayer 22. The multiple layers may be formed in the manner described inconnection with particle 10, or the photoconductor layer may beevaporated onto the glass bead. Ahead diameter of 3 to 30 microns, aphotoconductive layer of 5 to 60 microns thickness and a dyed layer of 4to 25 microns thickness will yield satisfactory particles in the 21 to250 micron diameter range.

FIG. 4 shows aparticle 24 comprising an inner capsule 26 containing aliquid dye 28, a photoconductor layer 20 and a dye layer or coating 22.The dye filled capsule 26 preferably in the diameter range of 3 to 20microns, may be produced in the manner described in US. Patents2,730,456, 2,730,457 and 2,714,074 issued to B. Green.

.The photoconductor layer may be added by evaporation the image.

. migrated or non-migrated and the [ye layer applied as described inconnection with Pros. 1 and 2.

FIG. 5 shows a. particle 30 comprising a colored glass or plastic bead32 covered with a thin layer 34 of aconducting material. In the case ofglass beadsalayer of fused transparent tin' oxide is suitable. In thecase of plastic heads a thin transparentlayer of evaporated metal ispreferred, although treatment with socalled anti-static solutions isalso suitable. Asshofwn inFIG. 6, it is also possible to producebeads'36 which comprise a solid, substantially spherical body 38 of tinoxide or other transparent electrically conducting materials which aresuitably colored in the mass, 7 As in the case of other parti-' cles adiameter of between 3 and 40* microns is preferred for particles of thisclass, although for some applications,largerparticles are suitable; v I

In the practice of color electroph'otography as set forth inthe presentinvention the following series of steps or their equivalent must beperformed in the approximate order shown: p I (1) Establishment of anelectrostatic field. (2) Production of a light image. p (3) Charging ordischarging of colored particles, which are in the electrostatic fieldand on which the light image is received, in accordance with the colorand pattern of (4) Migration ofeit-her the charged orthe dischargedplate 40 carries a transparent electrically conducting layer 42 of thinevaporated metal. NESA glass, made by the Pittsburgh Plate Glass Co.,which carries a transparent conducting layer of tin oxide or the likemay also be used.

I particles" of step 3, corresponding to the image, to'a new v An upperelectrode plate 44 spaced from plate 40 by any suitable distance from 1or'2 millimeters to several centimeters, carries at its lower surface aparticle receiving layer 46 to be described below. A suitable source 48of DC. voltage, connected to layer 42 andelectrode, 44 is provided withsuitable switching means 50. A negative potential of from 300 volts to5000 volts is applied to electrode 44 depending upon its spacing fromplate 40 and the characteristics of the particlesemployed.

In this arrangement primary color particle's 10 and 16 of the typeshownin FIGS. 1, 2 and 3, colored red,

green and blue, are employed; A substantially uniform layer of theseparticles is placed on conducting glass 42.

For purposes, of illustration a single layer is shownin FIG. 7; thelayer may be 3 or more particles deep and areas of .the originalsubject.

4 ticles may be immobilized bymeans adhesive overlay. W

If desired, surface 46 may, constitute an adhesive layer supported on asuitable base sheet in which case it becomes the image support. Theimage which remains on surface 42 is a negative'image, also of theadditive type and may be also transferred to a black base. This I of atransparent may be the desired image if color reversal is a requirementof the process.

As shown in the arrangement of FIGS. 9 and 10 this method can also beadapted to subtractive color photography. Here the arrangement ofelectrodes is similar to that ofFIGS. 7 and 8 and the pants have beennumbered correspondingly. In this modification, transparent primarycolored particles 52 of the type'shown in FIG.

4 are employed, containing cyan, magentaand'yellow dye at centers 28 andcolored red, green and blue respectively at layers 32. Initiallyparticles 52 are randomly distributed on surface 42 in a layer 3 to 4particles deep,

although in FIG. 9 they are shown in a single layer with regulardistribution for the purpose of explanation. when subjected to a lightimage some of the particles Wlll be moved upwardly depending upon thecolor 'of light.

Where red strikes a red jacketed particle 24 containing cyan dye restingon surface. 42 the resistance of the photoconductive layer is reduced,the particle becomes charged and migrates to surface 46. The.photoconductive layer of a blue jacketed yellow containing particlestruck by red light will remain unchanged in electrical resistance andwill not acquire a charge from surface 42 and will not migrate. Neitherwill a green jacketed magenta con taining particle mignate when struckby redlight. Blue light will cause blue jacketed yellow containingparticles to migrate while leaving the red and green jacketed particlesunmoved,and green light will cause green acketed magenta containingparticles to migrate while leaving the cyan and yellow jacketedparticles unmoved. Exposure 7 to white light causes panticles of'all'three jacket colors to migrateto surface 46. Following exposure the redacketed cyan containing panticl'es, blue jacketed yellow ccntainingparticles and green jacketed magenta containing particles willdelineateon surface 46 red, blue and green These particles are transferred,preferably by electrostatic means, to a transparent base or to awhiteie'flective base coated with a suitable transparent absorbentlayer, such as gelatin. A similar sheet is laid over the. particlecarrying surface, absorbing surface'in contact with the particles, andthe resulting sandwich subjected topressure as, for example, by passingbetween a pair of rollers. The pressure causes the particles to burst,and the dye previously contained within them is absorbed by theabsorlbent surf-ace of the base material. The two base layersarestripped apart and the particles of debris removed by means of brushingor washing. The resulting image will be a color'reversal'of theoriginal.

can'b e applied by simply cascadingonto surface 42, or

by spraying, or by applying with a roller.

i-After exposure to light of various colors the particles 'inigrate tothe position shown in FIG. 8. Where red, green and blue light reachsurface 42, the red, green and blue particles, respectively, migrate tosurface Where S White light reaches surface 42 particles of all threecolors migrate, while at the non-illuminated; areas there is nomigrationof particles. The imagewhich results on surface 46 is apositive image of the additive type, which for proper viewing as' aprint must be transferred to a black base, for example a sheet of blacksurfaced paper or plastic material. The image maybe transferred to sucha base by the usual'electrostatic means or through actionof a suitableadhesive layer. Fixing of the image may be accomplished by heating thesurface to cause -fusion and bonding of the-particle surface or the par-If the transfer is made from surface 42 after exposure the resultingcolor. image will be a positive color photograph. 7

FIGS. 11 to 14 illustrate still another way in which the invention maybe employed to produce subtractive color images. Here the particles 34are non photoconductive and possess the characteristics described. inconnection with FIGS. Sand '6. A layer of particles 34, 3 m4 deep,

is deposited on a photoconductive layerfitl of selenium-or -othersuitable material supported on an electrically conducting base 62 ofbrass, aluminum or the like which'is connected to one-terminal of avoltage source such as described in connection with FIG. 7. Spaced fromand 7 parallel to the surface 60 is a sheet of glass 64 carrying at itsunder side a layer 66 of transparent electrically conducting materialwhich is connected to the second terminal of the high voltage source.The layer of particles is exposed by light passing downwardly throughsheet 64- and conductive layer 66 onto particles 34. For

a given color or spectral band'of exposing light one or more of headcolors, which are cyan, magenta or yellow, will transmit the light tothe selenium layer below. The selenium layer thereupon becomesconducting, the transmitting bead becomesv charged and migrates upwardlyto layer 66.

As shown in FIG. 12, red, green and blue light exposure results inmigration of magenta and yellow, cyan and yellow, and cyan and magentaparticles, respectively, to :form subtractive color layers. In order toassure that the particles apply themselves in substantially layer formit is preferred that the sizes and conductivities of theparticles becontrolled. By making the cyan particles somewhat smaller and utilizinga relatively lower conductivity surface 38 over the core, theseparticles will migrate first to form a cyanlayer. By increasing the sizeof the magenta particles and increasing the electrical resistivity oftheir surface the magenta particles will migrate next to form the secondlayer. Preferably the yellow particles are the largest'and-possess thehighest resistivity, thereby being deposited last. While thediagrammatic representation in the drawing has been that of a singlelayer for thesake of simplicity, it should be borne in mind thatmultiple layers of the type described represent the actual structure.Where white light reaches the particle layer all particles migrate tosurface 66. Where no light strikes the particle layer no particlesmigrate. 1

The intermediate image appearing on surface 66 is next used for printingasshown in FIGS. 13 and 14. The image on surface '66 is projected onto aselenium plate 7072, similar to plate 60-62, through a'transparentconducting plate 7476 similar to plate 6466 onto color particles 34.During exposure these particles migrate to, surface 76 to form asubtractive color imagecorresponding to the original subject of FIG. 11.

FIGS. 15 and 16 show one means for employing color particles for theproduction of color photographs. A transparent plate 64 carrying atransparent conductive layer 66, such as shown in FIGS. 7 to is spacedaway from and parallel to a grid 80.- Layer'66 and grid 80 aremaintained at a suitable potential difference by a connection to asource 48of high voltage through a reversing switch-50. Spaced awayfrorn the opposite surface of grid 80 and parallel thereto is a particledistribution head indicated generally at 82, consisting of spaced apartplates 84 which form a series of alternate duct areas 86 and 88. Ductareas 86 are connected to a supply chamber 90 while ducts -88are'cori'nected to a pair of return chambers 92. An airblast shown byarrow 94 carries mixed color particles, such as those showninFIGS. 1,2and 3, into duct areas 86, through screen 80" and against layer 66 in adirection generally perpendicular to the latter. The appropriatelycolored particles are charged by their passage through the grid andadhere to layer 66, forming the color image in the manner described.Particles which remain inactive," because of their non-response to lightof a wavelength to which their resistance remains unchanged, are drawninto duct areas 88, through chamber 92, and returned as indicated byarrow 96 to a receiving chamber, not shown. The color particles on layer66 are transferred to a black paper or plastic base and are there fixedby heat or other well known means. 1

FIG. 17 shows diagrammatically a continuous color print machineemploying color particles.

. trode 114; the image at 116 moves synchronously with belt 100 and web106.

An endless, belt 100 of electrically conducting flexible material car-Layer 102 receives a charge of color particles such as that shown inFIGJS from a hopper-like distributor 118 which cascades the particlesonto the belt, the angle of repose of the latter being such that only asuflicient depth of particles is retained, the remainder being carriedaway for reuse through'duct 120. Layer 102 is cleaned of unusedparticles by means of a rotary brush 122, and the unused particles areretained in chamber 124 for reclassification and reuse. Reclassificationof the particles into threeportions, each containing a single color isaccomplished in a fashion analogousto the color process itself, i.e. bysuccessive exposure of the particles, while on a photoconductivesurface, to light of a given color.

The continuous printer shown in FIGS. 18 and 19 employs a rotarytransparent drum of glass or suitable plastic and carrying on its outersurface a transparent conductive coating 13-2. The drum is supportedthrough a plate 134 and bearing members 136 and 138 by a solid shaft140. The outer end of shaft 140 is rigidly attached to a base member 142which supports the entire printer.

Drum 130 is rotated by means of pulley 144, belt 146 and pulley 148driven by motor 150. The inner end of shaft 1'40 fixedly supports anexposure station base plate 152 on which is mounted a light housing 154provided with a light source 156 and condensers 158. A film gate 160,preferably curved, and a projection lens 162 lie on a common axis withthe light source and condensers. The transparency to be printed is shownin the form of a web 164 fed from a supply reel 166 to a takeup reel168, the rate of feed being controlled by a sprocket 170. Sprocket 1170is driven synchronously with drum 130 by bearing member 138 throughgears 172 and 174 sorthat the moving image of the web 164 is stationarywith respect to the outer surface 132 of the. drum. A tray 176,.preferablyof electrically nonconduct-ive material, contains a mixture178 of color developer particles of the type shown in FIG. 4 suspendedin a liquid dielectric such as light mineral oil or carbontetrachloride. One terminal of high voltage source 48 connects throughswitch 50 to conductive coating :132 and the second terminal connects to'a fine mesh electrode 180' submerged in mixture 178 and spaceduniformly from layer 132. The spacing can be in the range of from 0.1mm..to*10 mm. depending upon particle size and concentration as well asthe potential being employed. 'An air squeegee 182 directs air againstthe surface of the drum to .rernove unwanted particles and to wholly orpartially dry the drum surface.

. A web or transparent plastic base material 184 is held in contact withthe drum by means of roller 186 and passes under 'a suitable fixingstation 188 before being taken up on reel 190. A brush 192removes'fromthe drum surface the debris of ruptured developer particlesprior to exposure. Ultrasonic generator 194 in the sump of the developertray 176 below electrode 180 causes the impingement of developerparticles against the drum in a direction substantially normal to thedrum surface.

In operation, the original on film 164 is imaged through the drum andonto the layer of particles between surface 132 and the grid 180, theimage moving at the same speed as the periphery of the drum. Particlesof the correct color are energized in accordance with the showing inFIGS. 9 and 10 and adhere to coating 132. Accidentally entrainedparticles are removed by the air jet 182, the developer particles areruptured by roller 186, and the color image is transferred to base 184and fixed by heat or similar means, as necessary, at station 188. Thecleaning action'of brush 192 insures that surface 132 is free ofcontaminating particles prior to exposure. From time to time the properrelationship of relative concentration of the color particles in themixture 178 must be restored by addition of the needed color or colors.

It is apparent that other arrangements of printer devices could beconstructed for utilizing the color developer particles and the methoddescribed herein 'by those skilled in the art. The printers are notlimited to the production printing of signs, labels, posters andreflective traffic signs. 5

I claim: 1. A device for producing color and coextensive with said firstelectrode, said secondelectrode being provided with perforations overits entire extent and being electrically insulatedfronsaid'fir-stelecelectrophotographs comprising a first non-photoconductiveelectrode trans- 1 parent to the colors of the visible spectrum, asecond non-v photoconductive electrode parallel to, spaced apart from ofcolor photographs but lend themselves well to the v trode, said twoelectrodes forming thercbetweena'deyelopment chamber, a developerhousing terminating, at the face of said second electrode oppositefrornthat adjacent said first electrode, means for projecting throughsaid first electrode and into the space between said firstlele ctrodeand said second electrode a coiored'light-i'mage, means for establishinga potential difference between said first and second electrode, motionimparting means within said jdevela oper housing for passing fluidsuspended photoconductive developer particles through said secondelectrode into said thereon .-a pattern corresponding to thel projectedimage, a

web of black colored image receiving material and means 1 fortransferring said pattern'of particles tosaid receiving material. i v a2. A device for the continuous' production 'ofjcolor electrophotographscomprising a cylindrical non-light sensitive electrode transparent tothe colors ofthe visible spectrum, a stationary perforated arcuate'electrode parallelto and spaced from said transparent electrode,

a developing chamber comprising the space betweensaid I electrodes,means withinsaid cylindrical electrode for projecting a moving image incolors throughs'aid trans parent electrode and into said developingchamber, means for rotating said cylinder,- a developer supply chambercontaining photoconductive color developer-particles suspended in aliquid dielectric, said supply chamber surrounding said developingchamber and filIin'g said developing chamber with developer particlesthrough the'perfo rations in said arcuate electrode, means forsynchronizing the movement of said vprojectedimage and themo'vernent 1of said transparent electrode to maintain 'said projected 7 imagestationary with respect' to saidtnan-sparent'electrode I and means forestablishing 'an' electricalpotential between said two eectrodes wherebydeveloper particles illumii-- nated by said moving image are selectivelyattracted onto said transparent electrodeto form thereon a patterncorresponding to the projected color image;

3. A device'for the continuous production of color electrophotographs asclaimed in 'claim 2, said developer development chamber, wherebyselectedi developer "-parfia cles migrate onto the surfaceof saidfirst-electrodeto form supply chamber including means for producing anoscil-.

latory motion of developer particles in afidirection sub: A

stantially perpendicular to said electrodes,

. 4. A device for the continuous production of color electrophotographsas claimed in claim 2. including a transfer station for transferringsaid developer image to an image receiving surface, r

5. A device for the continuous production of color electnophotographs asclaimed in claim 4, including airsqueegee means for removing unwanteddeveloper particles from said transparent electrode prior totransferring said d lop i 6. A device for producing colorelectrophotographs comprising a fixed electrode transparent to thecolors oi the visible spectrum, a photoconductive surface movableparallel to and spaced apart from saidelectrode to form 1' therebet-weena developing chamber, a layer of transparent image-receiving materialcarried by said electrode and having one surface forming one side of thedeveloping chamber, a voltage source for maintaining an electricalpotential between said electrode and said photoconductive surface,meansfor depositing onsaid photoconductive surface a multiple layer ofdeveloper particles 5513C: tively responsive to light of differentcolors and means for projecting a light image in color through saidtransparent electrode and ir'nagereceiving material and through saiddeveloper particles onto said photoconductive survtace', whereby saiddeveloper particlesmigrate to said image-receiving material to formthereon a pattern correspending to said light image. 7 device forproducing color electrophotographs as clalmed in claim 6, saidphotoconductive material being the formof an endless belt.

2 8. A device for producing color electrophotographs as claimed in claim'6, said image receiving material, said photoconductive material andsaid light image moving (synchronously to maintain integrity of thepattern produced by the developer.

References Cited in the file of this patent UNITED STATES PATENTS SsP15, 1,952

1. A DEVICE FOR PRODUCING COLOR ELECTROPHOTOGRAPHS COMPRISING A FIRST NON-PHOTOCONDUCTIVE ELECTRODE TRANSPARENT TO THE COLORS OF THE VISIBLE SPECTRUM, A SECOND NONPHOTOCONDUCTIVE ELECTRODE PARALLEL TO, SPACED APART FROM AND COEXTENSIVE WITH SAID FIRST ELECTRODE, SAID SECOND ELECTRODE BEING PROVIDED WITH PERFORATIONS OVER ITS ENTIRE EXTENT AND BEING ELECTRICALLY INSULATED FROM SAID FIRST ELECTRODE, SAID TWO ELECTRODES FORMING THEREBETWEEN A DEVELOPMENT CHAMBER, A DEVELOPER HOUSING TERMINATING AT THE FACE OF SAID SECOND ELECTRODE OPPOSITE FROM THAT ADJACENT SAID FIRST ELECTRODE, MEANS FOR PROJECTING THROUGH SAID FIRST ELECTRODE AND INTO THE SPACE BETWEEN SAID FIRST ELECTRODE AND SAID SECOND ELECTRODE A COLORED LIGHT-IMAGE, MEANS FOR ESTABLISHING A POTENTIAL DIFFERENCE BETWEEN SAID FIRST AND SECOND ELECTRODE, MOTION IMPARTING MEANS WITHIN SAID DEVELOPER HOUSING FOR PASSING FLUID SUSPENDED PHOTOCONDUCTIVE DEVELOPER PARTICLES THROUGH SAID SECOND ELECTRODE INTO SAID DEVELOPMENT CHAMBER, WHEREBY SELECTED DEVELOPER PARTICLES MIGRATE ONTO THE SURFACE OF SAID FIRST ELECTRODE TO FORM THEREON A PATTERN CORRESPONDING TO THE PROJECTED IMAGE, A WEB OF BLACK COLORED IMAGE RECEIVING MATERIAL AND MEANS FOR TRANSFERRING SAID PATTERN OF PARTICLES TO SAID RECEIVING MATERIAL. 